1. Field of the Invention
The present invention refers to an image analyzer for adjusting a printer, which is used for producing photographic prints, with regard to a colour composition of the exposure light which is to be emitted by an exposure means of said printer and, if necessary, a sharp focus as well as, if necessary, an f-number and/or an exposure time according to the generic clause of patent claim 1.
2. Description of the Related Art
Such an image analyzer, which is known e.g. from the applicant's German patent 35 27 853, includes a video image converter device for recording an original exposed by the exposure means of the printer. The video image converter device is connected to a monitor via a circuit used for adjusting the colour and the brightness of the image converter signal. In the case of negative originals, this colour adjustment circuit comprises a colour reversal circuit. After a calibration of the overall arrangement, which is carried out only once, the known image analyzer permits a reliable determination of the colour composition and, if necessary, of the brightness or of the exposure time of the exposure light which is to be used for a specific negative or positive, said reliable determination being possible on the basis of an adjustment of the colour mixing head of the printer in such a way that the monitor image produced shows the desired colours. However, the respective adjustment will in any case require intervention of an operator as well as an operator's expert eye as far as the judgement of the colours of the monitor image is concerned.
For the purpose of automatically determining the colour value and the brightness of the exposure light used for producing the print in a printer, video analyzers are nowadays used, which determine--without intervention of an operator--the colour value, which is to be used for a specific original, as well as the exposure time of the exposure light. Such video analyzers are also referred to as autoscanners. An autoscanner comprises an exposure device for exposing the original, which will normally be a negative or a transparent original, as well as a scanning device, which can, for example, be a video camera, for recording the original. The scanning device has connected thereto a computer. A specific number of measuring points is examined by the scanning device with regard to brightness and colour values under the control of a computer program. This information is used for deriving therefrom the colour value for the exposure light of the printer as well as the exposure time and the brightness of said exposure light. For carrying out this derivation or calculation, an autoscanner will need a predetermined data set for each type of film. If a negative is underexposed or overexposed or incorrectly developed or incorrectly stored, its mask dyes will, however, change, and this will have the effect that the data set which has once been determined for a specific type of film will no longer be applicable to this type of film. This will also have the effect that the values, which were determined by the known autoscanner and which are used for adjusting the printer when a print is being exposed, are no longer correct. An additional disadvantage of such autoscanners is to be seen in the fact that such apparatuses are systems which are sold at quite a substantial price in the range of more than one hundred thousand German marks so that middle-class photographic firms cannot afford to work with such autoscanners.